Deactivation and regeneration studies of a PdSb/TiO2 catalyst used in the gas-phase acetoxylation of toluene
Deactivation and regeneration studies of a PdSb/TiO2 catalyst used in the gas-phase acetoxylation of toluene
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DOI：
10.1016/j.jcat.2011.06.005
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发表时间：
2011-08
影响因子：
7.3
通讯作者：
N. Madaan;S. Gatla;V. N. Kalevaru;J. Radnik;B. Lücke;A. Brückner;Andreas Martin
中科院分区：
文献类型：
--
作者：
N. Madaan;S. Gatla;V. N. Kalevaru;J. Radnik;B. Lücke;A. Brückner;Andreas Martin
采用PdSb/TiO2催化剂，甲苯（Tol）选择性气相乙酰氧基化合成乙酸苄酯（BA）。催化剂的初始活性较低，随反应时间延长，活性逐渐升高，在反应6h后达到最大值。催化剂在接下来的25 h内表现出稳定的性能，然后开始迅速失活。碳分析指出焦炭沉积是催化剂活性损失的主要原因。在250 ° C下再生可以恢复催化剂活性，但在随后的运行中再次显示出快速失活。在300 ° C下的再生处理不仅在恢复性能方面而且在保持催化剂相对良好的稳定性方面更加有效。然而，发现在350 ° C和更高温度下的处理在恢复催化活性方面无效。催化剂的这种令人惊讶的行为用各种技术如XRD、TEM和XPS分析详细研究。XRD数据证明Pd反射向较低的2 θ值移动，并分成两部分，指向不同类型的Pd物种。如XPS分析所揭示的，Pd0/PdO的表面比为1似乎对于更好的性能是必不可少的。令人惊讶的是，该比率在失活的催化剂中显著改变。此外，只有金属Pd物种被发现在该失活固体的催化剂表面上。此外，300 ° C再生可以在较大程度上恢复PdO浓度，而350 ° C再生不能恢复PdO比例。这种行为也被认为是在350 ° C下失活催化剂的非生产性再生的原因之一。此外，Pd0、PdO和Sb协同作用对于催化剂的稳定和高性能是必需的。
A PdSb/TiO2catalyst was subjected to selective gas-phase acetoxylation of toluene (Tol) to benzyl acetate (BA). The catalyst showed low initial activity, which increased with time and displayed maximum activity after 6h on-stream. The catalyst exhibited stable performance for the next 25h on-stream and then started to deactivate rapidly. Carbon analysis pointed to coke deposition as a main reason for the loss of catalytic activity. Regeneration at 250°C could restore the catalyst activity but showed rapid deactivation again in a subsequent run. Regenerative treatment at 300°C was much more effective not only in restoring the performance but also in maintaining relatively good stability of the catalyst. However, treatment at 350°C and higher was found to be ineffective in restoring catalytic activity. This surprising behavior of the catalyst was studied in detail with various techniques such as XRD, TEM, and XPS analysis. XRD data give evidence on shifting of Pd reflection to lower 2θ values and the splitting into two parts pointing to different types of Pd species. The surface ratio of Pd0/PdO of 1 seems to be essential for better performance as revealed by XPS analysis. Surprisingly, this ratio is significantly changed in the deactivated catalyst. Moreover, only metallic Pd species were found on the catalyst surface of this deactivated solid. In addition, regeneration at 300°C could restore PdO concentration to a greater extent, while the one regenerated at 350°C could not restore the PdO proportion. This behavior is also believed to be one of the reasons for the unproductive regeneration of deactivated catalyst at 350°C. Furthermore, Pd0, PdO, and Sb synergy is needed for stable and high performance of the catalyst.